Field of the Invention
The invention relates to a device and a method for adjusting an inductance of an electric conductor, in particular an electric conductor for connecting a feeding source to a primary winding structure of a system for inductive power transfer to a vehicle.
Desription of Related Art
Electric vehicles, in particular a track-bound vehicle, and/or a road automobile, can be operated by electric energy which is transferred by means of an inductive power transfer. Such a vehicle may comprise a circuit arrangement, which can be a traction system or a part of a traction system of the vehicle, comprising a receiving device adapted to receive an alternating electromagnetic field and to produce an alternating electric current by electromagnetic induction. Furthermore, such a vehicle can comprise a rectifier adapted to convert an alternating current (AC) to a direct current (DC). The DC can be used to charge a traction battery or to operate an electric machine. In the latter case, the DC can be converted into an AC by means of an inverter.
The inductive power transfer is performed using two sets of e.g. three-phase winding structures. A first set is installed on the ground (primary windings or primary winding structure) and can be fed by a wayside power converter (WPC). The way-sided elements of the inductive power transfer system can also be referred to as primary-sided elements.
The second set of windings is installed on the vehicle. For example, the second set of windings can be attached underneath the vehicle, in the case of trams under some of its wagons. For an automobile it can be attached to the vehicle chassis. The second set of windings is often referred to as pick-up-arrangement or receiver. The vehicle-sided elements of the inductive power transfer system can also be referred to as secondary-sided elements.
The first set of windings and the second set of windings form a high frequency transformer to transfer electric energy to the vehicle. This can be done in a static state (when there is no movement of the vehicle) and in a dynamic state (when the vehicle moves). In particular in the case of road automobiles, a stationary primary unit comprises a plurality of elements which are often arranged spatially separated.
The system for inductive power transfer has resonance circuits, e.g. for generating the power transfer field. These resonant circuits comprise inductivities and capacities, wherein the capacities are mostly provided by capacitors. Inductivities are provided by e.g. choking coils or by windings, in particular the aforementioned primary windings.
In addition to the primary winding structure, a primary-sided electric circuit can e.g. comprise an electric connecting network for electrically connecting the primary winding structure and a feeding source for providing an operating voltage/current to the primary winding structure.
This electric connecting network can comprise inductivities and capacities. Further, the electric connecting network can comprise at least one electric conductor which provides at least a part of the electric connection between the feeding source and the primary winding structure. Thus, the inductivity of a primary-sided electric circuit or a part thereof can be provided by an inductivity of said electric conductor.
It is further desirable to tune the high frequency transformer in order to maximize the amount of power transferred by the inductive power transfer. The tuning of the inductive power transfer system can comprise adjusting inductances and/or capacitances on the primary and/or the secondary side in order to minimize a reactive power generated by the inductive power transfer system.
It has been known to provide so called compensating capacitances, e.g. on the secondary side, in order to tune a resonant frequency of the secondary-sided resonant circuit to an operating frequency of the inductive power transfer system.
Changing electric parameters of electric components of the inductive power transfer system, however, usually requires a high labour-intensity, e.g. for opening a housing of the primary-sided system or the receiving device, in particular during a final adjustment during installation of the inductive power transfer system.
Other approaches use active elements such as switches in order to connect additional capacitors or inductors to an electric circuit for varying a total capacitance or total inductance.
WO 99/30402 discloses an inductor apparatus, wherein a ferrimagnetic core comprising one or ferrite elements having a “C”-shape or modified toroidal ferrite core including an air gap is threaded over about 1 turn of litz wire.